Manufacture of coated metal containers



Patented Jan. 31, 1939 MANUFACTURE OF COATED METAL CONTAINERS Loy s. Engle, Jackson Heights, Long Island, N. Y.,

assignor to Interchemical Corporation, a corporation of Ohio No Drawing. Application July 10, 1936 Serial No. 90,027

6 Claims.

This invention relates to the manufacture of coated metal food containers, and more particularly to the manufacture of tin cans lined with a thin Varnish, resin, lacquer or the like.

The purpose of lining cans or other metal con- .tainers is, of course, to form an impermeable coating which willprevent the contents of the containers from coming in contact with the metal. Accordingly, it is particularly important to avoid injury to the coating prior to the time the contents are sealed in the containers or cans, for the coating compositions commonly employed for this purpose are delicate and rather easily damaged.

On this account, one proposal has been to bend the containers or cans into shape, and subsequently apply the varnish or other coating composition to the interior walls of the containers, but this involves difficulties in the application of the coating materials, and not infrequently results in a coating which is permeable or otherwise defective.

On the other hand, if the metal is coated before it is bent to shape, the dies and other machinery, which shape the metal, often break the coating during the forming operations. Moreover, incident to these operations, a rather high degree of heat is developed, which also has to be reckoned with.

In order to assist in preventing such damage to the coating, oil may be applied to the coated surface, but this involves the disadvantage that the oil is dimcult to remove, and when any of it remains on the inside walls of the containers it imparts a foreign flavor or odor to many types of foodstufis subsequently packed in the containers.

According to the present invention, an improved method of making coated or lined cans or other metal containers is provided, in which method the coating material is applied to the metal and covered with a water-miscible liquid containing glycerine or the like and having a sufficiently low surface tension to form a continuous film on the coating, whereafter the coated metal is bent to shape, the liquid serving as a lubricant and protecting the coating against damage by the dies or forming members of the machinery. Subsequently, the water-miscible liquid may be readily removed, for instance by a stream of water.

Another feature of the present invention lies in the provision of an improved lubricant composition for present purposes.

While the composition of the lubricant for the coated surface in this process may vary considerably, I have found that excellent results are setinuous film, and which at the same time has a number of other advantages. For this purpose, I prefer to employ glycerine mixed with a small amount of a wetting agent. This composition is particularly satisfactory, inexpensive, and easy to apply. It is nonetoxic', odorless and tasteless, does not decompose or dissolvev ingredients in usual coating compositions such as varnishes, resins, lacquers or the like, is capable of forming a continuous film on such coatings, has especial ability to reduce friction at high temperatures encountered during manufacturing operations, and can readily be washed off afterwards by water.

I prefer to employ the composition in dilute form, and a mixture of the same with .water will ordinarily produce satisfactory results, provided the proportion of glycerine is suficient to reduce the surface tension of the water to a point where a continuous oily film is formed. For instance, a mixture of about 90 parts by weight of water and about 7 parts by weight of glycerine, together with a fraction of a part of wetting agent, produces good results. However, the glycerine may comprise an even larger proportion of the mixture, for instance as much as 50 to 60 per cent. of the total lubricant. Above this point, it is somewhat more difficult to wash off the glycerine and the composition is more expensive, but the invention in its broader aspects is not limited to particular proportions of water and glycerine. Although glycerine is especially advantageous for present purposes, other substances with similar characteristics may be substituted. Examples'of equivalents are polyhydric alcohol or glycols such as diethylene glycol or trlethylene glycol. v

I have found that for best results the surface tension of the lubricant employed should be less than about 40 dynes per centimeter at C., and'preferably less than about 36 dynes per centimeter at this temperature.

It is important to employ a wetting agent. Various wetting agents may be used in the composition, forexample, a sulphonatedester of a higher alcohol, such as Alphasol OT, a product manufactured and sold by American Cyanamid & Chemical Co., which is a sulphonated ester of alcohol containing 12 to 14 carbon atoms. The wetting agent may be employed in the order of a fraction of a per cent. ofthe total mixture, about .04 per cent. to .3 per cent. of it producing good results, and insuring continuity of lubricating film even after volatile ingredients (-mentioned belowl'have evaporated.

It is advantageous to incorporatein the-mixture .a volatile ingredient whichevaporates at the temperatures produced by the forming dies; the

form to provide a more effective lubricating acnon-volatile glycerineremaining in concentrated g point where some of the volatile ingredients of tion. For this purpose, I prefer to employ a few per cent. of ethyl alcohol, althoughit is not essential in some cases. The use of alcohol also increases the volatility of the mixture, causing the same to thicken at temperatures below the boiling point of water, and thus leaving a superior lubricating film at high temperatures. Although alcohol produces the effect of forminga continuous film by reducing the surface tension of the water-and-glycerine mixture, still it must be employed in large quantities (over 15%) to accomplish this, and when so used might soften the coating. Also, it leaves the film under the influence of increased temperature and then ceases to have the desired film-forming effect.

By way of example, I have found that the following composition is particularly effective for lubricating coated metal surfaces during bending operations:

Parts by weight Water-miscible lubricantglycerine 7.25 Diluent--water 90.4 Fluidity increasing agentethyl alcohol 2.3 Wetting agentAlphasol OT This mixture has a surface tension of 30.4 dynes per square centimeter at 25 0., when tested on a De Nuoy tensiometer made by Central Scientific Company of Chicago.

As indicated above, the mixture may be considerably more concentrated, or in other words the water content may be only about 25 per cent. or less of the total weight of the mixture. The

other ingredients are preferably employed in the general ratio of about 3 parts of glycerine to 1 part of alcohol to a small fraction of a part of wetting agent.

It will be appreciated that the coated metal, in passing through various parts of the machinery, particularly the shaping dies, may be heated to a the lubricant, such as alcohol and water, are evaporated. Temperatures of 70 C. are often encountered. In this situation, the present lubricant composition is particularly satisfactory because the evaporation of the volatile ingredients leaves the non-volatile glycerine or the like in concentrated form where its lubricating effect is increased rather than decreased. For such circumstances, it is important to employ the glycerine or the like in sufiicient amount to insure the presence of a continuous film on the coated surface during bending operations, even though some of the volatile ingredients evaporate.

Through the present invention, many advantages are secured. For instance, the lubricating agent is inexpensive, non-toxic, odorless and tasteless. It has excellent film forming ability and can be readily sprayed onto the coated metal, thus forming a welldistributed, homogeneous, continuous and stable lubricant film of desired thickness on the surface during bending opera--' tions. At the temperatures encountered in these operations, the present composition furnishes a. satisfactory lubricating action and does not vola- On the other hand, after the con-.

the lubricant should accidentally remain on the surface, it would not impart a disagreeable taste or flavor to the contents of the container. Thus it is possible to lubricate the inside surface of the can end which is last applied to close the can, and then apply it to form the finished can. Dam age to the coating, which might occur even with the relatively slight distortion incident to these steps, is thus avoided. The present lubricant does not tend to dissolve substances such as synthetic phenol-formaldehyde resins, cellulose nitrate, vinyl resins,,g1yptal resins, oil varnishes or the like, in' the compositions for coating the metal surfaces, and hence does not injure such coating compositions.

The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and de-. scribed, or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.

What I claim is:-

1. The method of shaping a coated metal article, which comprises the step of subjecting the coated metal covered with a lubricant containing a mixture of ordinary alcohol and water .which is volatile at operating "temperatures and .least a portion of the volatile mixture is evaporated.

2. The method of manufacturing a coated metal article which comprises applying to the hardened coated surface of the metal an aqueous lubricant, the essential active ingredient of which is awater-miscible oily material which is inert to the coating and foodstuffs, and thereupon shaping the coated rnetal.

3. The method of manufacturing a coated metal can for food-stuffs which comprises applying to the hardened coated surface of the metal an aqueous lubricant, the essential active ingredient of which is a water-miscible oily material which is inert to the coating and foodstuffs, thereupon shaping the coated metal by means of hot dies which evaporate a'portion of the water in the lubricant, and thereafter removing the balance of the lubricant.

4. Themethod of forming coated metal articles which comprise applying a thin layer of coating composition to the surface of the metal, enabling said coating to harden, applying to the hardened coating an aqueous lubricant which is mostly water and the essential active ingredient of which is a polyhydric alcohol which is inert to the coating and foodstuffs, thereupon shaping the metal, and subsequently removing said lubricant.

5. The method as claimed in claim 4 wherein said essential ingredient is glycerine and wherein said lubricant also contains a minute amount of a wetting agent.

6. The method as claimed inclaim 4 wherein said lubricant is composed essentially of glycerine and water containing a minute amount of a wetting agent and a few percent. of ordinary alcohol, said glycerine constituting a small proportion of the lubricant, and being present in amount 'such that the surface tension of the lubricant is less than about 40 dynes per centimeter at 25 C.

LOY S. ENGLE. 

